1. Field of the Invention
This invention relates to multiple tires mounted parallel to each other on an outer periphery of a single wheel. These multiple tires have superior safety and operability. This invention relates particularly to multiple tires that communicate with each other through an airflow pipe inserted into an internal space of each tire. Further, the airflow pipe comprises a pneumatic pressure control valve that is effective, either open or closed, in responding to an air leak in the multiple tires.
2. Description of the Prior Art
FIG. 12 shows a sectional view of a single pneumatic tire 3 for a vehicle. Tire 3 is mounted on a rim 2 of a wheel 1. FIG. 13 shows a section view of two tires 3, 3 mounted parallel to each other on two rims 2a, 2b of single wheel 1. This technique is disclosed in Japanese Laid-open Patent Publication No. 60-12303. It was developed specifically for a sports car to overcome the disadvantages of a single tire having a larger width. The two tires have good water repelling properties, more area to contact the ground, less vibration, and more stability when driven. In addition, even if one tire blows out, the driver can drive the car on the other normal tire without coming to a stop.
However, when one tire leaks air gradually, the driver drives on without becoming aware of the leak. In particular, when the car travels in a straight line, it drives almost normally. Moreover, if an inner tire leaks air, it is very hard to detect from the outside. However, when one of the tires is leaking air and the car goes around a curve at a high speed, a serious accident can occur, because the car's center of gravity is disturbed by the leaking tire. Though multiple tires have certain advantages, they are not widely used because of these safety considerations.
In U.S. Pat. No. 1,134,701 issued to Seeburger, a valve is incorporated in a wheel to allow air from one tire to flow into the other tire. The valve is normally open to allow air to pass from one tire to the other freely, thereby equalizing pressure between the two tires. The valve has a frictionally restrained closure device that closes if the pressure difference between the two tires reaches a specified level. If one of the tires develops a small leak, air from one tire can flow into the other. However, if the leak is such that the specified pressure difference develops, the valve closes and the sound tire is isolated from the leaking tire.
The Seeburger device suffers from the following limitations. The frictional engagement of the valve closure device does not permit the valve to reopen when the pressures are approximately equalized. Thus, if the leaking tire is repaired, for example, by an emergency flat-fixing product, the valve will remain closed until a high pressure is applied to the once-leaking tire. This restorative pressure must be substantially greater than that in the sound tire. In fact, this restorative pressure would have to be as great as the specified pressure that caused the valve to close in the first place, and the excess pressure would have to be applied for a precise time interval to prevent the valve from overshooting and closing on the opposite side. In addition, the large pressure required to shift the valve closure to the neutral position could result in unsafe pressure conditions in the once-leaking tire. Such a large pressure may be impossible to achieve under certain circumstances, for example, in an emergency.
The Seeburger arrangement allows pressure between the two tires to equalize when the pressure differences are smaller than a certain pressure difference and to close once, when the pressure differences are greater than the certain pressure difference. Thus the Seeburger device is, for all practical purposes, a one-shot device for protection against blowouts in one tire. It also has the disadvantage that, should a small leak develop in one tire, both the leaky tire and the sound tire could lose all their air and become completely flat. Seeburger's apparatus therefore cannot solve the problem solved by the present invention of quickly alerting a driver to a leak and letting him drive on safely.
Another inter-tire valve arrangement is shown by Cardi in U.S. Pat. No. 2,789,617. The Cardi valve is actually two valves, one for each tire, each of which opens to the other tire when the pressure in the respective tire is above a fixed level. The air presses against a spring which allows air to flow out of the tire and into a common space. As long as the pressure in either tire is above the fixed level, the corresponding valve will remain open to pass air to the other tire until equilibrium is reached. Both valves remain open as long as both tires are at or above the fixed pressure level. Should a leak cause pressure in one tire to drop below the fixed level, the other tire will feed the leaky tire until the pressure in the sound tire reaches the fixed level. Thereafter, the valve of the sound tire will close and the sound tire will remain indefinitely at the fixed pressure level.
The Cardi valve is able to prevent a sound tire from becoming flat. However, when a rapid loss of pressure occurs in one tire, such as in a blowout, the Cardi valve permits a rapid loss of pressure from the sound tire. This sudden change of pressure can be dangerous, since the loss of pressure causes a sudden change in the vehicle's handling characteristics. In addition, when both tires are inflated above the fixed pressure level, air passes between the tires because of minute transient pressure differences between them. Such minute transient pressure differences occur when the vehicle hits bumps, swerves, or turns. The pumping of air between tires through the valve, which restricts the flow of air, is also a source of energy loss that increases fuel consumption.
For the above reasons, Cardi's apparatus cannot solve the problem solved by the present invention of safely alerting a driver to a leak and letting him drive on. Moreover, Cardi's device introduces certain undesirable parasitic energy losses.